Apparatus for electronically controlling internal combustion engine

ABSTRACT

An apparatus for electronically controlling an internal combustion engine of automobiles, in which a processor comprising a CPU, a RAM and a ROM is determined to be in the state of its normal operation when the processor delivers a predetermined pulse train in response to an interrupt signal having a predetermined period and supplied to the processor, and in which a backup circuit is actuated by a discriminant signal indicating the abnormal operation of the processor so that the operation of controlling the internal combustion engine, normally performed by the processor, is performed by the backup circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention relates to subject matter described in the following applications:

U.S. Ser. No.: 943,930; Filed: Sept. 20, 1978; Hiroastu Tokuda et al.Iadd., now U.S. Pat. No. 4,276,601; .Iaddend.

U.S. Ser. No.: 951,509; Filed: Oct. 16, 1978; Shigeki Morinaga et al.Iadd., now abandoned; .Iaddend.

U.S. Ser. No.: 952,275; Filed: Oct. 18, 1978; Masao Takato et al.Iadd., now U.S. Pat. No. 4,280,189; .Iaddend.

U.S. Ser. No.: 952,276; Filed: Oct. 18, 1978; Hiroastu Tokuda et al.Iadd., now U.S. Pat. No. 4,277,829; .Iaddend.

U.S. Ser. No.: 952,279; Filed: Oct. 18, 1978; Hiroastu Tokuda et al.Iadd., now U.S. Pat. No. 4,309,759; .Iaddend.

U.S. Ser. No.: 952,531; Filed: Oct. 18, 1978; Masumi Imai et al.Iadd., now U.S. Pat. No. 4,312,038; .Iaddend.

U.S. Ser. No.: 952,532; Filed: Oct. 18, 1978; Hiroastu Tokuda et al.Iadd., now U.S. Pat. No. 4,274,141; .Iaddend.

U.S. Ser. No.: 952,533; Filed: Oct. 18, 1978; Masumi Imai et al.Iadd., now U.S. Pat. No. 4,282,573; .Iaddend.

U.S. Ser. No.: 011,845; Filed: Feb. 13, 1979; Toshio Furuhashi et al.Iadd., now U.S. Pat. No. 4,310,888; .Iaddend.

U.S. Ser. No.: 059,029; Filed: July 19, 1979; Sanshiro Obara et al.Iadd., now U.S. Pat. No. 4,276,602; .Iaddend.

U.S. Ser. No.: 060,751; Filed: July 26, 1979; Toshio Furuhashi et al.Iadd., now U.S. Pat. No. 4,296,722; .Iaddend.

U.S. Ser. No.: 064,431; Filed: Aug. 7, 1979; Toshio Furuhashi.Iadd., now U.S. Pat. No. 4,274,142; .Iaddend.

U.S. Ser. No.: 073,085; Filed: Sept. 6, 1979; Masumi Imai et al.Iadd., now U.S. Pat. No. 4,408,279. .Iaddend.

.Iadd.BACKGROUND OF THE INVENTION .Iaddend.

This invention relates to an apparatus for electronically controlling an internal combustion engine for automobiles, especially provided with a device for detecting a fault in an electronic processor and a backup circuit.

The continuing demand for automobiles as modes of transportation has caused several social problems. Examples are air pollution and the consumption of petroleum as fuel.

Recently, some countermeasures have been taken to reduce poisonous substances in exhaust gases, but this has caused a degradation of the overall efficiency of the internal combustion engine (hereafter referred to as the engine).

For preventing the degradation of the operating efficiency of the engine and for improving the countermeasures against exhaust gases, an electronic control apparatus has come to be employed which has an improved control precision. For example, there have been proposed an electronically controlled fuel injection apparatus and an electronically controlled ignition timing apparatus, and most recently an ignition apparatus controlled by a microprocessor.

In the conventional control apparatus, mechanical controls are merely, in general, replaced by electric controls and therefore the individual controlled objects must be provided with the associated electronic control units.

The control of an engine should also reduce the poisonous components in exhaust gases and operate the engine with a high efficiency. The assembly of the separate electronic control units provided for the controlled objects, as described above, has a poor interrelation among the control units so that a close control of the overall control system is impossible. Moreover, such a composite control system must be accompanied by very complicated circuits. For example, the circuit, used in the system, for detecting the irregular output of a sensor such as an angular position sensor becomes very complicated.

.Iadd.SUMMARY OF THE INVENTION .Iaddend.

An object of this invention is to detect a fault in an electronic processor by means of a simple circuit.

Another object of this invention is to provide a backup circuit for controlling fuel injection and ignition lead angle in place of the failed processor in response to a signal representing a fault in the processor.

According to one aspect of this invention, there is provided an electronic control apparatus for an internal combustion engine, including therein a processor comprising a central processing unit, a random access memory and a read-only memory, registers for storing input and output signals and a comparator for comparing the contents of one of the registers with the contents of another, said apparatus comprising a means for generating by the use of said registers and said comparator a signal having a predetermined period for causing an interrupt with respect to said processor and means for determining the processor to be in the state of its normal operations when said processor generates a signal equivalent to a pulse train having a pulse duration substantially equal to the predetermined period.

.Iadd.BRIEF DESCRIPTION OF THE DRAWINGS .Iaddend.

The above and other objects, features and advantages of the present invention will be more clear from the following description with reference to the accompanying drawings, in which:

FIG. 1 shows an arrangement plan of sensors and actuators in an embodiment of an electronic engine control apparatus;

FIG. 2, including A-G, is a diagram for explaining the operation of the circuits shown in FIG. 1;

FIG. 3 shows the detail of the control circuit shown in FIG. 1;

FIG. 4 shows a partial detail of the input/output circuit shown in FIG. 3;

FIG. 5, including A-.[.I.]..Iadd.L.Iaddend., is a diagram for explaining the operation of the circuit shown in FIG. 4;

FIG. 6 shows the detail of the stage counter shown in FIG. 4;

FIG. 7 shows in detail concrete examples of the reference and the instantaneous register groups shown in FIG. 4;

FIG. 8 shows in detail concrete examples of the first and the second comparison output register groups 502 and 504;

FIG. 9 shows in detail a synchronizing circuit;

FIG. 10, including A-I, is a diagram for explaining the operation of the circuit shown in FIG. 9;

FIG. 11 shows in detail a concrete example of the incrementor 478 shown in FIG. 4;

FIGS. 12A and 12B show in detail an incrementor controller;

.[.FIG. 13 shows.]. .Iadd.FIGS. 13A-E show .Iaddend.the waveforms useful in explaining the processing of the fuel injection signal;

FIG. 14, including A-.[.E.]..Iadd.F.Iaddend., shows the waveforms useful in explaining the ignition timing control;

FIG. 15, including A-C, shows the waveforms useful in explaining the processing by EGR or NIDL;

FIG. 16, including A-D, shows the signal waveform useful in explaining the detection of the rotational speed RPM of engine or the speed VSP of vehicle;

FIG. 17 shows a circuit of a fault detecting device for determining a fault in the processor, as an embodiment of this invention;

FIG. 18, including A-F, shows waveforms useful in explaining the operation of the circuit shown in FIG. 17;

FIG. 19 is a flow chart illustrating the processing by the circuit shown in FIG. 17 when an interrupt is caused to occur;

FIGS. 20A and 20B show a STATUS register and a discrete I/O circuit with their holding signals;

FIG. 21 shows in block diagram a backup circuit applied to the control of fuel injection;

FIG. 22 shows in block diagram form a backup circuit applied to the control of ignition lead angle;

FIG. 23 shows a specific example of the backup circuit used in the circuit shown in FIG. 21 or 22; and

FIG. 24 shows a specific example of the backup circuit used in the circuit shown in FIG. 21.

.Iadd.DETAILED DESCRIPTION .Iaddend.

The electronic engine control apparatus will now be described by way of an embodiment with the aid of attached drawings. FIG. 1 shows the main structure of an electronic engine control apparatus. Air sucked in through an air cleaner 12 is passed through an air-flow meter 14 to measure the flow rate thereof and the air-flow meter 14 delivers an output QA indicating the flow rate of air to a control circuit 10. A temperature sensor 16 is provided in the air-flow meter 14 so as to detect the temperature of the sucked air and the output TA of the sensor 16, indicating the temperature of the sucked air, is also supplied to the control circuit 10.

The air flowing through the air-flow meter 14 is further passed through a throttle chamber 18, an intake manifold 26 and a suction valve 32 to the combustion chamber 34 of an engine 30. The quantity of air inhaled into the combustion chamber 34 is controlled by changing the aperture of a throttle valve 20 provided in the throttle chamber 18 and interlocked with an accelerator pedal 22. The aperture of the throttle valve 20 is detected by detecting the valve position of the throttle valve 20 by a throttle valve position detector 24 and the signal QTH representing the valve position of the throttle valve 20 is supplied from the throttle valve position detector 24 to the control circuit 10.

The throttle chamber 18 is provided with a bypass 42 for idling the engine and an idle adjust screw 44 for adjusting the flow of air through the bypass 42. When the throttle valve 20 is completely closed, the engine is operated in the idling condition. The sucked air past the air-flow meter flows via the bypass 42 and drawn into the combustion chamber 34. Accordingly, the flow of the air sucked in under the idling condition is changed by adjusting the idle adjust screw 44. The energy created in the combustion chamber 34 is determined substantially depending on the flow rate of the air drawn through the bypass 42 so that the rotational speed of the engine under idling condition can be adjusted to be optimal by controlling the flow rate of air drawn into the combustion chamber by adjusting the idle adjust screw 44.

The throttle chamber 18 is also provided with another bypass 46 and an air regulator 48. The air regulator 48 controls the flow rate of the air through the bypass 46 in accordance with the output signal NIDL of the control circuit 10, so as to control the rotational speed of the engine during the warming-up operation and to properly supply air into the combustion chamber at a sudden change, especially a sudden closing, in the valve position of the throttle valve 20. The air regulator 48 can also change the flow rate of air during the idling operation.

Next, the fuel supply system will be described. Fuel stored in a fuel tank 50 is sucked out to a fuel damper 54 by means of a fuel pump 52. The fuel damper 54 absorbs the pressure undulation of the fuel supplied from the fuel pump 52 so that fuel having a constant pressure can be supplied through a fuel filter 56 to a fuel pressure regulator 62. The fuel past the fuel pressure regulator 62 is sent by pressure to a fuel injector 66 through a fuel pipe 60 and the output INJ of the control circuit 10 causes the fuel injector 66 to be actuated to inject the fuel into the intake manifold 26.

The quantity of the fuel injected by the fuel injector 66 is determined by the period during which the fuel injector 66 is opened and by the difference between the pressure of the fuel supplied to the injector and the pressure in the intake manifold 26 into which the pressurized fuel is injected. It is however preferable that the quantity of the injected fuel should depend only on the period for which the injector is opened and which is determined by the signal supplied from the control circuit 10. Accordingly, the pressure of the fuel supplied by the fuel pressure regulator 62 to the fuel injector 66 is controlled in such a manner that the difference between the pressure of the fuel supplied to the fuel injector 66 and the pressure in the intake manifold 26 is always kept constant in any driving condition. The pressure in the intake manifold 26 is applied to the fuel pressure regulator 62 through a pressure conducting pipe 64. When the pressure of the fuel in the fuel pipe 60 exceeds the pressure upon the regulator 62 by a predetermined level, the fuel pipe 60 communicates with a fuel return pipe 58 so that the excessive fuel corresponding to the excessive pressure is returned through the fuel return pipe 58 to the fuel tank 50. Thus, the difference between the pressure of the fuel in the fuel pipe 60 and the pressure in the intake manifold 26 is kept always constant.

The fuel tank 50 is also provided with a pipe 68 connected to a canister 70 provided for the suction of vaporized fuel or fuel gas. When the engine is operating, air is sucked in through an open air inlet 74 to send the fuel gas into the intake manifold 26 and therefore into the engine 30 via a pipe 72. In the case of stopped engine, the fuel gas is exhausted through active carbon filled in the canister 70.

As described above, the fuel is injected by the fuel injector 66, the suction valve 32 is opened in synchronism with the motion of a piston 75, and a mixture gas of air and fuel is sucked into the combustion chamber 34. The mixture gas is compressed and fired by the spark generated by an ignition plug 36 so that the energy created through the combustion of the mixture gas is converted to mechanical energy.

The exhaust gas produced as a result of the combustion of the mixture gas is discharged into the open air through an exhaust valve (not shown), an exhaust pipe 76, a catalytic converter 82 and a muffler 86. The exhaust pipe 76 is provided with an exhaust gas recycle pipe 78 (hereafter referred to as an EGR pipe), through which a part of the exhaust gas is fed into the intake manifold 26, that is, the part of the exhaust gas is circulated to the suction side of the engine. The quantity of the circulated exhaust gas is determined depending on the aperture of the valve of an exhaust gas recycle apparatus 28. The aperture is controlled by the output EGR of the control circuit 10 and the valve position of the apparatus 28 is converted to an electric signal QE to be supplied as an input to the control circuit 10.

A λ sensor 80 is provided in the exhaust pipe 78 to detect the fuel-air mixture ratio of the mixture gas sucked into the combustion chamber 34. An oxygen sensor (O₂ sensor) is usually used as the λ sensor 80 and detects the concentration of oxygen contained in the exhaust gas so as to generate a voltage V.sub.λ corresponding to the concentration of the oxygen contained in the exhaust gas. The output V.sub.λ of the λ sensor 80 is supplied to the control circuit 10. The catalytic converter 82 is provided with a temperature sensor 84 for detecting the temperature of the exhaust gas in the converter 82 and the output TE of the sensor 84 corresponding to the temperature of the exhaust gas in the converter 84 is supplied to the control circuit 10.

The control circuit 10 has a negative power source terminal 88 and a positive power source terminal 90. The control circuit 10 supplies the signal IGN, for causing the ignition plug 36 to spark, to the primary winding of an ignition coil 40. As a result, a high voltage is induced in the secondary winding of the ignition coil 40 and supplied through a distributor 38 to the ignition plug 36 so that the plug 36 fires to cause the combustion of the mixture gas in the combustion chamber 34. The mechanism of the firing of the ignition plug 36 will be further detailed. The ignition coil 40 has a positive power source terminal 92 and the control circuit 10 also has a power transistor for controlling the primary current through the primary winding of the ignition coil 40. The series circuit of the primary winding of the ignition coil 40 and the power transistor is connected between the positive power source terminal 92 of the ignition coil 40 and the negative power source terminal 88 of the control circuit 10. When the power transistor is conducting, electromagnetic energy is stored in the ignition coil 40 and when the power transistor is cut off, the stored electromagnetic energy is released as a high voltage to the ignition plug 36.

The engine 30 is provided with a temperature sensor 96 for detecting the temperature of the water 94 as coolant in the water jacket and the temperature sensor 96 delivers to the control circuit 10 a signal TW corresponding to the temperature of the water 94. The engine 30 is further provided with an angular position sensor 98 for detecting the angular position of the rotary shaft of the engine and the sensor 98 generates a reference signal PR in synchronism with the rotation of the engine, e.g. every 120° of the rotation, and an angular position signal each time the engine rotates through a constant, predetermined angle (e.g. 0.5°). The reference signal PR and the angular position signal PC are both supplied to the control circuit 10.

In the system shown in FIG. 1, the air-flow meter 14 may be replaced by a negative pressure sensor. Such a negative pressure sensor 100 is depicted by dashed line and the negative pressure sensor 100 will supply to the control circuit 10 a voltage VD corresponding to the negative pressure in the intake manifold 26. A semiconductor negative pressure sensor is practically used as such a negative pressure sensor 100. One side of the silicon chip of the semiconductor is acted on by the boost pressure of the intake manifold while the atmospheric or a constant pressure is exerted on the other side of the chip. The constant pressure may be vacuum as the case may be. With this construction, a voltage VD corresponding to the pressure in the intake manifold is generated, which is to be supplied to the control circuit 10.

FIG. 2 illustrates the relationships between the firing timing and the crank angular position and between the fuel injection timing and the crank angular position, where a six-cylinder engine is used. In FIG. 2, diagram A represents the crank angular position and indicates that a reference signal PR is delivered by the angular position sensor 98 every 120° of the crank angle. The reference signal PR is therefore supplied to the control circuit 10 at 0°, 120°, 240°, 360°, 480°, 600°, 720° etc. of the angular position of the crank shaft.

Diagrams B, C, D, E, F and G correspond respectively to the 1st cylinder, the 5th cylinder, the 3rd cylinder, the 6th cylinder, the 2nd cylinder and the 4th cylinder. J₁ -J₆ designate respectively the periods for which the suction valves of the corresponding cylinders are open. The periods are shifted by 120° of crank angle from one another. The beginning and the durations of the periods at which the suction valve is open are generally as shown in FIG. 2 though somewhat different depending upon the type of engine used.

A₁ -A₅ indicate the periods for which the valve of the fuel injector 66 is open, i.e. fuel injection periods. The lengths JD of the periods A₁ -A₅ can be considered to be the quantities of fuel injected at a time by the fuel injectors 66. The injectors 66, provided for the respective cylinders, are connected in parallel with the drive circuit in the control circuit 10. Accordingly, the signal INJ from the control circuit 10 opens the valves of the fuel injectors 66 simultaneously so that all the fuel injectors 66 simultaneously inject fuel. Now, the first cylinder will be taken as an example for description. The output signal INJ from the control circuit 10 is applied to the fuel injectors 66 provided respectively in the manifold or inlet ports of the respective cylinders in timing with the reference signal INTIS generated at 360° of crank angle. As a result, fuel is injected in by the injector 66 for the length JD of time calculated by the control circuit 10, as shown at A₂ in FIG. 2. However, since the suction valve of the 1st cylinder is closed, the injected fuel at A₂ is not sucked into the 1st cylinder, but kept stagnant near the inlet port of the 1st cylinder. In response to the next reference signal INTIS generated at 720° of crank angle, the control circuit 10 again sends a signal to the respective fuel injectors 66 to perform the fuel injections as shown at A₃ in FIG. 2. Simultaneously almost with the fuel injections, the suction valve of the 1st cylinder is opened to cause the fuel injected at A₂ and the fuel injected at A₃ to be sucked into the combustion chamber of the 1st cylinder. The other cylinders will be also subjected to similar series of operations. For example, in case of the 5th cylinder corresponding to the diagram C, the fuel injected at A₂ and A₃ is sucked in at the period J₅ for which the suction valve of the 5th cylinder is opened. In case of the 3rd cylinder corresponding to the diagram D, a part of the fuel injected at A₂, the fuel injected at A₃ and a part of the fuel injected at A₄ are sucked in together while the suction valve is open for the period J₃. The part of the fuel injected at A₂ plus the part of the fuel injected at A₄ equals a quantity of fuel injected by a fuel injector at a single actuation. Therefore, also during the suction step of the 3rd cylinder, the quantity of fuel equal to the total quantities supplied through double actuations of the fuel injector will be sucked in. Also, in case of the 6th, 2nd or 4th cylinder as shown in the diagram E, F or G, the double quantity of fuel is sucked in during a single step of suction. As apparent from the above description, the quantity of fuel determined by the fuel injection signal INJ from the control circuit 10 is equal to half the quantity of fuel to be sucked into the combustion chamber. Namely, the necessary quantity of fuel corresponding to the quantity of air sucked into the combustion chamber 34 will be supplied through the double actuations of the fuel injector 66.

Throughout the diagrams A to G in FIG. 2, G₁ -G₆ indicate the ignition times associated respectively with the 1st to 6th cylinders. When the power transistor provided in the control circuit 10 is cut off, the primary current of the ignition coil 40 is interrupted so that a high voltage is induced across the secondary winding. The induction of the high voltage takes place in timing with the ignition epochs G₁, G₅, G₃, G₆, G₂ and G₄. The induced high voltage is distributed to the spark plugs provided in the respective cylinders by means of a distributor 38. Accordingly, the spark plugs of the 1st, 5th, 3rd, 6th, 2nd and 4th cylinders fire successively in this order to inflame the combustible mixture of fuel and air.

FIG. 3 shows an example of the detail of the control circuit 10 shown in FIG. 1. The positive power source terminal 90 of the control circuit 10 is connected with the positive electrode 110 of a battery to provide a voltage VB for the control circuit 10. The power source voltage VB is adjusted to a constant voltage PVCC of, for example, 5 volts by a constant voltage circuit 112. This constant voltage PVCC is applied to a central processor unit (hereafter referred to as CPU), a random access memory (hereafter referred to as RAM) and a read-only memory (hereafter referred to as ROM). The output PCVV of the constant voltage circuit 112 is supplied also to an input/output circuit 120.

The input/output circuit 120 includes therein a multiplexer 122, an analog-digital converter 124, a pulse output circuit 126, a pulse input circuit 128 and a discrete input/output circuit 130.

The multiplexer 122 receives plural analog signals, selects one of the analog signals in accordance with the instruction from the CPU, and sends the selected signal to the A/D converter 124. The analog signal inputs applied through filters 132 to 144 to the multiplexer 122 are the outputs of the various sensors shown in FIG. 1; the analog signal TW from the sensor 96 representing the temperature of the cooling water in the water jacket of the engine, the analog signal TA from the sensor 16 representing the temperature of the sucked air, the analog signal TE from the sensor 84 representing the temperature of the exhaust gas, the analog signal QTH from the throttle aperture detector 24 representing the aperture of the throttle valve 20, the analog signal QE from the exhaust recycle apparatus 28 representing the aperture of the valve of the apparatus 28, the analog signal V.sub.λ from the λ sensor 80 representing the air-excess rate of the sucked mixture of fuel and air, and the analog signal QA from the air-flow meter 14 representing the flow rate of air. The output V.sub.λ of the λ sensor 80 above is supplied through an amplifier with a filter circuit to the multiplexer 122.

The analog signal VPA from an atmospheric pressure sensor 146 representing the atmospheric pressure is also supplied to the multiplexer 122. The voltage VB is applied from the positive power source terminal 90 to a series circuit of resistors 150, 152 and 154 through a resistor 160. The series circuit of the resistors 150, 152 and 154 is shunted with a Zener diode 148 to keep the voltage across it constant. To the multiplexer 122 are applied the voltages VH and VL at the junction points 156 and 158 respectively between the resistors 150 and 152 and between the resistors 152 and 154.

The CPU 114, the RAM 116, the ROM 118 and the input/output circuit 120 are interconnected respectively by a data bus 162, an address bus 164 and a control bus 166. A clock signal E is supplied from the CPU to the RAM, ROM and input/output circuit 120 and the data transfer takes place through the data bus 162 in timing with the clock signal E.

The multiplexer 122 of the input/output circuit 120 receives as its analog inputs the cooling water temperature TW, the temperature TA of the sucked air, the temperature TE of the exhaust gas, the throttle valve aperture QTH, the quantity QE of recycle exhaust gas, the output V.sub.λ of the λ sensor, the atmospheric pressure VPA, the quantity QA of the sucked air and the reference voltages VH and VL. The quantity QA of the sucked air may be replaced by the negative pressure VD in the intake manifold. The CPU 114 specifies the address of each of these analog inputs through the address bus 164 in accordance with the instruction program stored in the ROM 118 and the analog input having a specified address is taken in. The analog input taken in is sent through the multiplexer 122 to the analog/digital converter 124 and the output of the converter 124, i.e. the digital-converted value, is held in the associated register. The stored value is coupled, if desired, to the CPU 114 or RAM 116 in response to the instruction sent from the CPU 114 through the control bus 166.

The pulse input circuit 128 receives as inputs a reference pulse signal PR and an angular position signal PC both in the form of a pulse train from the angular position sensor 98 through a filter 168. A pulse train of pulses PS having a repetition frequency corresponding to the speed of the vehicle is supplied from a vehicle speed sensor 170 to the pulse input circuit 128 through a filter 172. The signals processed by the CPU 114 are held in the pulse output circuit 126. The output of the pulse output circuit 126 is sent to a power amplifying circuit 186 and the fuel injector 66 is controlled by the output signal of the power amplifying circuit 186.

Power amplifying circuits 188, 194 and 198 respectively control the primary current of the ignition coil 40, the aperture of the exhaust recycle apparatus 28 and the aperture of the air regulator 48 in accordance with the output pulses of the pulse output circuit 126. The discrete input/output circuit 130 receives signals from a switch 174 for detecting the completely closed state of the throttle valve 20, from a starter switch 176, and from a gear switch 178 indicating that the transmission gear is in the top position, respectively through filters 180, 182 and 184 and holds the signals. The discrete input/output circuit 130 also receives and holds the processed signals from the central processor unit CPU 114. The discrete input/output circuit 130 treats the signals the content of each of which can be represented with a single bit. In response to the signal from the central processor unit CPU 114, the discrete input/output circuit 130 sends signals respectively to the power amplifying circuits 196, 200, 202 and 204 so that the exhaust recycle apparatus 28 is closed to stop the recycle of exhaust gas, the fuel pump is controlled, the abnormal temperature of the catalyzer is indicated by a lamp 208 and the overheat condition of the engine is displayed by a lamp 210.

FIG. 4 shows in detail a concrete example of the pulse output circuit 126. A register group 470 comprises reference registers which serve to hold the data processed by the CPU 114 and the data representing the predetermined fixed values. These pieces of data are transferred from the CPU 114 to the reference register group 470 through the data bus 162. Each of the registers is specified through the address bus 164 to receive and hold the associated data.

A register group 472 comprises instantaneous registers which serve to hold the instantaneous states of the engine and the associated mechanisms. The instantaneous register group 472, a latch circuit 476 and an incrementor 478 form a counter.

An output register group 474 comprises, for example, a register 430 for holding the rotational speed of the engine and a register 432 for holding the vehicle speed. The registers 430 and 432 hold the values by taking in the contents of the instantaneous registers when certain conditions are satisfied. Each register of the output register group 474 is selected by the signal sent from the CPU 114 through an address bus and the content of the selected register is sent to the CPU 114 through the data bus 162.

A comparator 480 receives, for comparison, at its input terminals 482 and 484 the reference data from selected registers of the reference register group and the instantaneous data from selected registers of the instantaneous register group. The result of the comparison by the comparator 480 is delivered at its output terminal 486. The output delivered at the output terminal 486 is set in the selected registers of a first comparison output register group 502 serving as a comparison result holding circuit, and then set in the corresponding registers of a second comparison output register group 504.

The operations of accessing, i.e. reading out of or writing in, the reference register group 470, the instantaneous register group 472 and the output register group 474, the operations of the incrementor 478 and the comparator 480, and the operations of setting the output of the comparator 480 in the first and second comparison output register groups 502 and 504 are all processed within a predetermined period of time. Other various processing operations are performed in a time sequential manner or in a time-division manner in accordance with the order of the stages instructed by a stage counter 572. In each stage, one of the registers constituting the reference register group 470, one of the registers of the instantaneous register group 472, one of the registers of the first comparison result register group 502, one of the registers of the second comparison result register group 504 and, if necessary, one of the registers of the output register groups 474 are selected. The incrementor 478 and the comparator 480 are used in common.

FIG. 5 shows diagrams useful in explaining the operation of the circuit in FIG. 4. The clock signal E, shown in the diagram A, is supplied from the CPU 114 to the input/output circuit 120. Two clock signals φ1 and φ2, as shown in the diagram B and C, having no overlap with each other are derived from the clock signal E by means of a pulse generating circuit 574. The circuit shown in FIG. 4 is operated by these clock signals φ1 and φ2.

The diagram D in FIG. 5 depicts a stage signal which is switched over during the rising transient of the clock signal φ2. The processing in each stage is performed in synchronism with the clock signal φ2. In FIG. 5, "THROUGH" indicates that the latch circuit and the register circuits are in their enabled conditions and that the outputs of these circuits depend on the inputs thereto. Also, "LATCH" means that these circuits hold certain data and that the outputs therefrom are independent of the inputs thereto.

The stage signal shown in the diagram D serves to read data out of the reference group 470 and the instantaneous register group 472, that is, to read out the contents of certain selected registers of the groups. The diagrams E and F represent the operations of the reference and instantaneous register groups 470 and 472, respectively. These operations are performed in synchronism with the clock signal φ1.

The diagram G indicates the operation of the latch circuit 476. The latch circuit 476 is in the THROUGH state when the clock signal φ2 is at high level, serving to take in the content of a particular register selected from among the instantaneous register group 472. When the clock signal φ2 is at low level, on the other hand, the latch circuit 476 is in the LATCH state. Thus, the latch circuit 476 serves to hold the content of the specific register of the instantaneous register group selected in accordance with the stage assumed then. The data held in the latch circuit 476 is increased or not on the basis of external conditions by means of the incrementor 478 operated out of timing with the clock signal.

The incrementor 478 performs the following functions in response to the signal from the incrementor controller 490. The first function is the function of incrementing, to increase by unity the value of the input data. The second is the function of non-incrementing, to pass the input without any change. The third is the function of resetting, to change the entire input into data representing the value 0 (zero).

As seen from the flow of data through the instantaneous register group 472, one register of the group 472 is selected by the stage counter 572 and the data held by the selected register is supplied to the comparator 480 through the latch circuit 476 and the incrementor 478. Further, there is provided a return loop for the signal from the output of the incrementor 478 to the selected register, a complete closed loop being formed. Therefore, since the incrementor has a function of increasing the data by unity, the closed loop functions as a counter. However, if the data delivered from the particular register selected from the instantaneous register group is again received by the particular register as an input by coming back through the return loop, an erroneous operation will easily take place. The latch circuit 476 is provided to block unwanted data. Namely, the latch circuit 476 assumes the THROUGH state in timing with the clock signal φ2 while the THROUGH state in which input data is to be written in the instantaneous registers is in timing with the clock signal φ1. Therefore, data is interrupted or cut at the offset between the clock signals φ1 and φ2. Namely, even if the content of any specific register of the group 472 is changed, the output of the latch circuit 476 remains unchanged.

The comparator 480, just like the incrementor 478, operates out of timing with the clock signals. The comparator 480 receives as its inputs the data held in a register selected from among the reference register group 470 and the data held in a register selected from among the instantaneous register group 472 and sent through the latch circuit 476 and the incrementor 478. The result of the comparison of both data is set in the first comparison result register group 502 which takes the THROUGH state in timing with the clock signal φ1. The set data is further set in the second comparison result register group 504 which assumes the THROUGH state in synchronism with the clock signal φ2. The outputs of the register group 504 are the signals for controlling the various functions of the incrementor and the signals for driving the fuel injectors, the ignition coil and the exhaust gas recycle apparatus.

Also, in response to the signals, the results of the measurements of the rotational speed of the engine and the vehicle speed are transferred from the instantaneous register group 472 to the output register group 474 in every stage. For example, in the case of writing the rotational speed of the engine, a signal indicating that a preset time has elapsed is held in the register RPMWBF 552 of the second comparison result register group 504 and the data held in the register 462 of the instantaneous register group 472 is transferred to the register 430 of the output register group 474 in response to the output of the register 552 in the RPM stage listed in the table 1 given later.

On the other hand, unless a signal indicating the elapse of the preset time is set in the register RPMWBF 552, the operation to transfer the data held in the register 462 to the register 430 never takes place even in the RPM stage.

The data held in the register 468 of the group 472 and representing the vehicle speed VSP is transferred to the output register 432 of the group 474 in response to the signal from the register VSPWBF 556 of the group 504 in the VSP stage.

The writing of the data representing the rotational speed RPM of the engine or the vehicle speed VSP in the output register group 474 is performed as follows. Reference should be had again to FIG. 5. When the stage signal STG is in the RPM or VSP mode, the data from the register 462 or 468 of the instantaneous register group 472 is written in the latch circuit 476 if the clock signal φ2 is at a high level, the latch circuit 476 takes the THROUGH state when the clock signal φ2 is at high level. And when the clock signal φ2 is at low level, the written data is in the latched state. The thus held data is then written in the output register group 474 in timing with the high level of the clock signal φ1 in response to the signal from the register RPMWBF 552 or VSPWBF 556 since the output register group 474 assumes the THROUGH state when the clock signal φ1 is at high level, as indicated at the diagram K of FIG. 5. The written data is latched at the low level of the clock signal φ1.

In the case of reading the data held in the output register group 474 by the CPU 114, the CPU 114 first selects one of the registers 430 and 432 of the group 474 through the address bus 164 and then takes in the content of the selected register in timing with the clock signal E shown in the diagram A of FIG. 5.

FIG. 6 shows an example of a circuit for generating the stage signal STG shown in the diagram D of FIG. 5. The contents of a stage counter SC570 or incremented in response to the signal φ1 sent from the pulse generating circuit 574 which is per se well-known. The outputs C₀ -C₆ of the stage counter SC570 and the outputs of the T register shown in FIG. 4 are supplied as inputs to a stage decoder SDC. The stage decoder SDC delivers as its outputs signals 01-017 and the signals 01-017 are written in a stage latch circuit STGL in timing with the clock signal φ2.

The reset input terminal of the stage latch circuit STGL receives a signal GO of bit 2° from the mode register shown in FIG. 4 and when the signal GO of bit 2° takes its low level, all the outputs of the stage latch circuit STGL are at the low level to stop all the processing operations. If, on the other hand, the signal GO resumes the high level, the stage signals STG are successively delivered again in the predetermined order to perform the corresponding processings.

The above stage decoder SDC can be easily realized by the use of, for example, a ROM (read-only memory). The table 1 given below lists up the details of the contents 00-7F of the stage signals STG delivered as outputs from the stage latch circuit STGL.

                  TABLE 1                                                          ______________________________________                                         (Hexadecimal)                                                                  C.sub.0 -                                                                           C.sub.3 -C.sub.6                                                          C.sub.2                                                                             0        1       23      4     5    67                                    ______________________________________                                         0    EGRP     INTL    CYL ADV DWL   VSP  RPM INJ                               1    NIDLP    INTL    CYL ADV DWL   VSP  RPM INJ                               2     --      INTL    CYL ADV DWL   VSP  RPM INJ                               3    RPMW     INTL    CYL ADV DWL   VSP  RPM INJ                               4    ENST     INTL    CYL ADV DWL   VSP  RPM INJ                               5     --      INTL    CYL ADV DWL   VSP  RPM INJ                               6     --      INTL    CYL ADV DWL   VSP  RPM INJ                               7     --      INTL    CYL ADV DWL   VSP  RPM INJ                               8    EGRD     INTL    CYL ADV DWL   VSP  RPM INJ                               9    NIDLD    INTL    CYL ADV DWL   VSP  RPM INJ                               A     --      INTL    CYL ADV DWL   VSP  RPM INJ                               B    VSPW     INTL    CYL ADV DWL   VSP  RPM INJ                               C    INTV     INTL    CYL ADV DWL   VSP  RPM INJ                               D     --      INTL    CYL ADV DWL   VSP  RPM INJ                               E     --      INTL    CYL ADV DWL   VSP  RPM INJ                               F      --     INTL    CYL ADV DWL   VSP  RPM INJ                               ______________________________________                                    

First, a general reset signal GR is received at the reset terminal R of the stage counter SC570 shown in FIG. 6 so that all of the outputs C₀ -C₆ of the stage counter SC570 become "0" (zero). The general reset signal is delivered from the CPU at the time of starting the control circuit 10. Under the above condition, if the clock signal φ2 is received, a stage signal EGRPSTG is delivered in timing with the rising transient of the signal φ2. According to the stage signal EGRPSTG, a processing EGRP is performed. Upon reception of a pulse of the clock signal φ1, the stage counter SC570 counts up to increase its content by unity and then the arrival of the clock signal φ2 causes the next stage signal INTLSTG to be delivered. A processing INTL is performed according to the stage signal INTLSTG. Thereafter, a stage signal CYLSTG is delivered for the execution of a processing CYL and then a stage signal ADVSTG for a processing ADV. In like manner, as the stage counter SC570 continues to count up in timing with the clock signal φ1, other stage signals STG are delivered in timing with the clock signal φ2 and the processings according to the stage signals STG are executed.

When all the outputs C₀ -C₆ of the stage counter SC570 become "1", a stage signal INJSTG is delivered for the execution of a processing INJ, which terminates the whole processings listed in the above table 1. Upon reception of the next clock signal φ1, all the outputs C₀ -C₆ of the stage counter SC570 becomes zero and the stage signal EGRPSTG is delivered again for the execution of the processing EGRP. In this way, the processings listed in the table 1 will be repeated.

The processings in the respective stages, listed in the table 1 will be detailed in the following table 2.

                  TABLE 2                                                          ______________________________________                                         Stage    Type of Processing Operation Corresponding to                         Signal   Stage Signal                                                          ______________________________________                                         EGRPSTG  to determine whether or not the period of time                                 determined by the data held in the register                                    418 has elapsed, so as to determine the period                                 of the pulse current for driving the valve                                     of the exhaust gas recycle apparatus.                                 INTLSTG  to determine whether or not the engine has                                     rotated through an angle corresponding to the                                  data held in the register 406, on the basis                                    of the reference signal PR form the angular                                    position sensor, so as to generate a reference                                 signal INTLS.                                                         CYLSTG   to determine whether or not the reference signals                              INTLS represented by the data held in the                                      register 404 have been generated, so as to                                     generate a signal CYL indicating a single                                      rotation of the crank shaft.                                          ADVSTG   to determine whether or not the engine has                                     rotated through an angle corresponding to                                      the data held in the register 414, on the                                      basis of the reference signal, so as to                                        generate an ignition timing signal.                                   DWLSTG   to determine whether or not the engine has                                     rotated through an angle corresponding to                                      the data held in the register 416, after                                       the generation of the immediately previous                                     reference signal, so as to generate a signal                                   indicating the initial conduction point of                                     the primary current through the ignition                                       coil.                                                                 VSPSTG   to hold, for detecting the vehicles speed,                                     the data corresponding to the actually                                         measured vehicle speed in the output register                                  when the lapse of a predetermined period                                       of time is ascertained on the basis of the                                     signal (output of VSPWBF) representing the                                     lapse of the predetermined period of time and                                  to continue to further count the vehicle                                       speed pulses when the predetermined period                                     of time has not yet elapsed.                                          RPMSTG   to hold, for detecting the rotational speed                                    of the engine, the data corresponding to                                       the actually measured vehicle speed in the                                     output register when the lapse of a predeter-                                  mined period of time is ascertained on the                                     basis of the signal (output of RPMBF) represent-                               ing the lapse of the predetermined period                                      of time and to continue to further count                                       the angular position signals when the pre-                                     determined period of time has not yet elapsed.                        INJSTG   to determine whether or not the time correspond-                               ing to the data held in the register 412 has                                   elapsed, on the basis of the signal CYL, so                                    as to produce a signal INJ representing the                                    valve opening period for the fuel injector.                           NIDLPSTG to determine whether or not the time correspond-                               ing to the data held in the register 422 has elapsed,                          so as to determine the period of the pulse                                     current for driving the air regulator.                                RPMWSTG  to determine whether or not a predetermined                                    period of time for which the pulses synchronous                                with the rotation of the engine are to be                                      counted has elapsed, so as to measure the                                      rotational speed of the engine.                                       ENSTSTG  to detect the condition that there is no                                       signal delivered from the angular position                                     sensor for a preset period of time, so as                                      to detect an accidental stopping of engine.                           EGRDSTG  to determine whether or not the duration of the                                pulse of the pulse current for driving the                                     valve of the exhaust gas recycle apparatus                                     has become coincident with the value corres-                                   ponding to the data held in the register 420.                         NIDLDSTG to determine whether or not the pulse duration                                 of the pulse current for driving the air                                       regulator has become coincident with the value                                 corresponding to the data held in the register                                 424.                                                                  VSPWSTG  to determine whether or not a preset period of                                 time for which the pulses synchronous with                                     the vehicle speed are to be counted has lapsed,                                so as to measure the vehicle speed.                                   INTVSTG  to determine whether or not the period of time                                 corresponding to the data held in the register                                 408 has elapsed.                                                      ______________________________________                                    

In the stage latch circuit STGL shown in FIG. 6, the circuit components associated with the output signals STG0 and STG7 serve to synchronize externally supplied signals with the clock signal produced in the input/output circuit 120. The output STG0 is delivered when all the outputs C₀ -C₂ of the stage counter SC570 are zero "0" while the output STG7 is delivered when all the outputs C₀ -C₂ are one "1".

Examples of the external signals are the reference signal PR generated in timing with the rotation of the engine, the angular position signal and the vehicle speed pulse signal PS generated in synchronism with the rotation of the wheel. The periods of these signals, which are pulse signals, vary to a considerable extent and therefore the signals, if not controlled, are by no means synchronous with the clock signals φ1 and φ2. Accordingly, there is no determination of whether the increment operation is performed or not, in the stage ADVSTG, VSPSTG or RPMSTG in the table 1.

It is therefore necessary to synchronize between the external pulse signal from, for example, a sensor and the stage of the input/output circuit. For the improvement in the detection accuracy, the angular position signal PC and the vehicle speed signal PS must have their rising and falling synchronized with the stage while the reference signal PR must have its rising edge synchronized with the stage.

FIG. 7 shows the details of the register groups 470 and 472.

First, the input of data to the reference register group will be described. Input data is supplied to a latch circuit 802 through the data bus 162. Simultaneously, a read/write signal R/W and a signal VMA are supplied from the CPU through the control bus 166. The registers in the input/output circuit are selected through the address bus 164. As is well known, a technique of selecting the registers is to decode the data sent through the address bus into the signals corresponding to the respective registers and the decoding is effected by an Address Decoder 804. The outputs of the decoder 804 are connected with the registers specified by the symbols labeled at the respective outputs (wiring is omitted). In accordance with the above mentioned read/write signal R/W, signal VMA and the address bus bit A15 corresponding to the input/output circuit, the select chip write and the select chip read signals CSW and CSR are sent through gates 806 and 808 respectively.

In the case of the writing of the data from the CPU, the select chip write signal CSW is delivered and applied to the input side of the registers. Now, the select chip read signal CSR is not delivered and therefore the gate 810 is closed and the tri-state buffer 812 is closed.

The data sent through the data bus 162 is latched by the latch circuit WDL 802 in timing with the clock signal φ2. The data latched in the latch circuit 802 is transferred through the write bus driver WBD to the respective registers of the reference register group 470 and written in the registers selected by the address decoder in timing with the signal φ1. The registers 408, 410, 412, 414, 416, 426 and 428 of the group 470 have 10 bits each and both the CPU and the data bus are designed to treat data of 8 bits, so that the upper two bits and the lower eight bits of the ten-bit data are given two different addresses. Accordingly, the transfer of data to the 10-bit register takes place twice per data.

On the other hand, the reading process is contrary to this. The chip select gate 808 is selected by the output sent through the control bus and the buffer 812 is opened by the output of the gate 810 in timing with the signal E. Since at this time a desired register is selected by the address signal sent through the address bus 164, the data in the selected register is delivered through the tri-state (three-state) buffer 812 onto the data bus 162.

Next, description will be made of the operation to select the reference register and the instantaneous register in accordance with the stage signal. The reference and instantaneous register groups 470 and 472 receive the stage signals. In response to the stage signals, the corresponding registers are selected in the respective stages. Of the reference register group 470, the registers 412, 414 and 416 do not receive the stage signals and therefore are not selected, when the corresponding outputs INJBF, ADVBF and DWLBF are delivered from the comparison result holding register group 504. Instead, when the signals INJBF, ADVBF and DWLBF are received, the zero register 402 is selected in the stages INJ, ADV and DWL. Concerning the instantaneous register group 472, the register 456 receives the stage signals EGRP and EGRD and the register 458 receives the stage signals NIDLP and NIDLD. Thus, the register 456 is selected together with the reference register 418 or 420 in the stage EGRPSTG or EGRDSTG, respectively. And the register 458 is selected together with the reference register 422 or 424 in the stage NIDLPSTG or NIDLDSTG, respectively.

FIG. 8 shows in detail the first and second comparison output register groups 502 and 504 shown in FIG. 4. The output of the comparator 480 is divided into a signal indicating an EQUAL condition and a signal indicating a LARGER condition and both the signals are sent to the NOR gate 832. Accordingly, the output of the NOR gate 832 indicates an EQUAL OR LARGER condition. Since the NAND gate 830 receives the EQUAL signal from the comparator 480 and the signal for selecting the ZERO register 402, the signal indicating the EQUAL condition is blocked by the NAND gate 830 is the ZERO register 402 is selected. As a result, the output of the NOR gate 832 is only the signal indicating the LARGER condition. It is necessary to select the respective registers of the first comparison output register group 502 in timing with the respective registers of the reference and instantaneous register groups. Therefore, the registers of the group 502 receives the clock signal φ1 and the corresponding stage signals to be set in synchronism with the corresponding reference and instantaneous registers. As a result, the result of comparison made in each stage is latched in the associated register of the first comparison output register group in timing with the clock signal φ1. Since the second comparison output register group 504 receives the clock signal φ2 for its set timing, the above result of comparison is set in the second comparison output register group in timing with the clock signal φ2 delayed with respect to the clock signal φ1. Then, the registers of the group 504 deliver their respective BF outputs.

The registers 512, 528, 552, 556, 516 and 520 of the second comparison output register group 504 are provided respectively with the waveform shaping circuits 840, 832, 844, 846, 848 and 850, which respectively deliver pulses INTLD, ADVD, RPMWD, VSPWD, INTVD and ENSTD performing their duties only during the period from the instant that the register group 504 is set to the next arrival of the stage signal ZEROSTG.

For the purpose of detecting the pulse train signals supplied from the various sensors to the input/output circuit, it is necessary to synchronize these pulse train signals with the operation of the input/output circuit. For, since the periods or the pulse durations of these pulse train signals vary depending on, for example, the rotational speed of the engine and the vehicle speed to considerable extents, each lengthened period may equal several times the period of the corresponding stage while each shortened period may be too short in comparison with that of the corresponding stage to exist until the corresponding stage signal is received. Therefore, if these pulse train signals are not suitably controlled, the exact counting of the pulse trains will be impossible.

FIG. 9 shows an example of a synchronizing circuit for synchronizing the external pulse train signals with the stage signals in the input/output circuit and FIG. 10 shows a timing chart useful in explaining the operation of the synchronizing circuit shown in FIG. 9.

The external input pulse signals from the various sensors, such as the reference pulses PR, the angular position signal PC and the vehicle speed signal PS are latched respectively in the latch circuits 600, 602, 604 in response to the output STG0 shown in FIG. 6.

In FIG. 10, the diagram A corresponds to the waveform of the clock signal φ2, B to the clock signal φ1, and C and D to the stage signals STG7 and STG0. These stage signals are generated in timing with the clock signal φ2. The signal waveform of the diagram E is of the output pulse from the angular position sensor or the vehicle speed sensor, corresponding to the reference pulse PR or the angular position pulse PC or the vehicle speed pulse PS. The time of occurrence, the duty cycle and the period of the signal shown in the diagram E are irregular, the signal being received independent of the corresponding stage signal.

Now, let it be assumed that the signal as shown in the diagram E is received by the latch circuits 600, 602 and 604. Then, they are latched in response to the stage signal STG0 (pulse S1 in diagram D). Accordingly, the outputs A1, A2 and A3 take the high level at an instant S2, as shown in diagram F. Also, since the input signals PR, PC and PS are at the high level when the stage signal STG0 represented by the pulse S3 is received, the high level is latched in the latch circuits 600, 602 and 604. On the other hand, since the input signals PR, PC and PS are at the low level when the stage signal STG0 represented by the pulse S4 is received, the low level is latched in the latch circuits 600, 602 and 604. As a result, the outputs A1, A2 and A3 of the latch circuits 600, 602 and 604 are as shown in the diagram F of FIG. 10. Since the latch circuits 606, 608 and 610 respectively latch the outputs A1, A2 and A3 of the latch circuits 600, 602 and 604 in response to the stage signal STG7 represented by the pulse S5 shown in the diagram C, the outputs B1, B2 and B3 of the latch circuits 606, 608 and 610 rise at the instant S6. Also, since they latch the high level when the stage signal STG7 represented by the pulse S7 is received, they continue to deliver the high level output. Therefore, the output signals B1, B2 and B3 of the latch circuit 606, 608 and 610 are as shown in the diagram G of FIG. 10.

The NOR circuit 612 receives the signal B1 and the inverted version of the signal A1 through the inverter 608 and delivers the synchronized reference signal PRS as shown in the diagram H of FIG. 10. This synchronized reference signal PRS is generated in response to the leading edge of the stage signal STG0 under the condition that the reference signal PR has changed from a low level to a high level and disappears in response to the leading edge of the stage signal STG7 and so has a pulse duration from the leading edge of the stage signal STG0 to the leading edge of the stage signal STG7. The exclusive OR circuits 614 and 616 receive the signals A2 and B2 and the signals A3 and B3. The signal S8 is generated in response to the leading edge of the stage signal STG0 when the stage signal STG0 is generated after the signal PC or PS is changed from a low to a high level and disappears in response to the leading edge of the stage signal STG7, while the signal S9 is generated in response to the leading edge of the stage signal STG0 when the signal STG0 is generated after the signal PC or PS is changed from a high to a low level and disappears in response to the leading edge of the stage signal STG7. The duty cycles of the signals S8 and S9 are equal to that of the signal shown in the diagram H of FIG. 10, and therefore determined by the stage signals STG0 and STG7.

In the above description, it is assumed that the signals PR, PC and PS have the same duty cycle and that they are simultaneously received. In practice, however, they have different duty cycles and are received at different instants. Further, each signal itself has its period and duty cycle varied with time.

The synchronizing circuit shown in FIG. 9 serves to render the irregular duration of the signal constant. The constant pulse duration is determined by the difference between the rising instants of the stage signals STG0 and STG7. Therefore, the pulse widths or durations can be controlled by controlling the stage signals supplied to the latch circuits 600, 602, 604, 606, 608 and 610.

The pulse durations are determined depending on the timing of the stages listed in the table 1. Namely, as seen from the table 1, the stage INTL corresponds to the condition that the outputs of the counters C₀ -C₂ and the outputs of the counters C₃ -C₆ are respectively 1 and 0, i.e. (C₀ -C₂, C₃ -C₆)=(1, 0) and further the conditions that (C₀ -C₂, C₃ -C₆)=(1, 1), (1, 2), (1, 3) . . . , thus the stage INTL appears every eighth stage.

Since each stage is processed in 1 μsec, the stage INTL appears every 8 μsec. In the stage INTL, the angular position signal PC must be detected to control the incrementor and when the output PC of the angular position sensor 98 is supplied to the synchronizing circuit shown in FIG. 9, the circuit generates the synchronizing pulses which coincide in timing with the stage INTL so that the incrementor controller is controlled by the synchronizing pulses PCS in the stage INTL.

The synchronizing pulse signal PCS is detected also in the stage ADV or RPM. The stage ADV or RPM appears whenever each of the values of the outputs C₃ -C₆ is incremented by unity while each of the values of the outputs C₀ -C₂ is 3 or 6, respectively. Each of the stages ADV and RPM reappears at a period of 8 μsec.

The signal STG0 shown in FIG. 9 is delivered when the values of the outputs C₀ -C₂ of the stage counter SC570 are 0 while the signal STG7 is delivered when the bits C₀ -C₂ have a decimal value of 7. The stage signals STG0 and STG7 are generated independent of the outputs C₃ -C₆. As seen from FIG. 10, the synchronized signal PCS necessarily has its pulse duration existing while the outputs C₀ -C₂ of the stage counter change from 0 to 6. The incrementor controller is controlled by detecting the signal in the stages INTL, ADV and RPM.

In like manner, the stage CYL for detecting the synchronized reference signal PRS takes place when the outputs C₀ -C₂ of the stage counter SC570 are 2. When the angular position sensor 98 delivers the reference pulse PR, it is necessary to deliver the synchronized reference signal PRS when the outputs C₀ -C₂ are 2. This requirement is satisfied by the circuit shown in FIG. 9 since the circuit delivers the pulse signal whose pulse duration lasts from the stage signal STG0 to the stage signal STG7.

The stage VSP for detecting the vehicle speed takes place only when the outputs C₀ -C₂ of the stage counter are 5. It is therefore only necessary to deliver the synchronized signal PSS while the outputs C₀ -C₂ are 5. This requirement is also satisfied by the circuit shown in FIG. 9 since with the circuit the outputs C₀ -C₂ have the values from 0 to 6. In the circuit shown in FIG. 9, the stage signals STG0 and STG7 may be replaced respectively by the stage signal STG4 delivered when the outputs C₀ -C₂ have the value of 4 and the stage signal STG6 delivered when the outputs C₀ -C₂ are 6. In this case, if the signal PS is received, the synchronized signal PSS is always delivered when the outputs C₀ -C₂ are 4 and 5.

Now, the cycles of the stages will be referred to. As shown in the above given table 1, 128 stage signals are produced corresponding to the values 0-127 of the outputs C₀ -C₆ of the stage counter SC570. When all these 128 stage signals have been generated, a major cycle is completed to be followed by a next major cycle. Each major cycle is constituted of 16 minor cycles and each minor cycle consists of 8 stage signals. The minor cycle corresponds to the values 0 to 7 of the outputs C₀ -C₂ of the stage counter and is finished in 8 μsec.

To exactly synchronize the pulse signals PR, PC and PS and to exactly generate the synchronized pulses PRS, PCS and PSS, it is necessary for the outputs of the sensors to have a pulse duration longer than the period of the minor cycle. For example, the duration of the angular position pulse PC is shortened as the rotational speed of engine increases. It is about 9 μsec. for 9000 rpm. It is therefore necessary to make the period of the minor cycle shorter than 9 μsec. so as to exactly perform the synchronizing operation even at 9000 rpm. In this embodiment, the period of the minor cycle is chosen to be 8 μsec.

FIG. 11 shows in detail an example of the incrementor 478 shown in FIG. 4. The input terminals A0-A9 respectively receive the 10-bit data from one of the registers of the instantaneous register group, selected in accordance with the corresponding stage signal.

First, description will be made of the bit A0, i.e. signal received at the input terminal A0. The bit A0 and the count signal is supplied to the exclusive OR circuit 850. If the bit A0 is 0 (zero) and the count signal has the zero (L) level, then the signal 0 (zero) is delivered by the circuit 850. On the other hand, if the bit A0 is 1 and the count signal is the L level, the value 1 is delivered. Namely, when the count signal is 0, the bit A0 is passed without any change.

If the count signal has the 1(H) level, the bit A0 is inverted; the output of the circuit 850 is 0 when the bit A0 is 1 and when the bit A0 is 0. With respect to the bit A0, the value is counted up by unity in accordance with the count signal. When the bit A0 and the level of the count signal are both 1, a carry signal is supplied to the processing gate 854 for the upper bit A1.

The NOR gate 852 serves to detect the above said carry signal and only when there is the carry signal, the bit A1 is inverted to be delivered as an output B1. When there is no carry signal, the output B1 is the same as the bit A1. In like manner, the NOR gates 856, 860, 864, 868, 872, 876, 880 and 884 detect the corresponding carry signals and the input bits A2-A9 are supplied, as inverted versions or without change, to the exclusive OR circuits 858, 862, 866, 870, 874, 878, 882 and 886. Namely, if there are the corresponding carry signals, the bits A2-A9 are inverted to form the outputs B2-B9, respectively. In the presence of the count signal, therefore, the input bits A0-A9 are each counted up by unity to produce the output signals B0-B9.

AND gates 890-908 serve as reset mechanisms. Upon reception of a reset signal, the outputs B0-B9 become all zero, irrespective of the outputs of the exclusive OR circuits 850-886. The count signal and the reset signal for controlling the incrementor whose detail is shown in FIG. 11 are generated by the incrementor controller 490 shown in FIG. 4.

FIGS. 12A and 12B show the details of the incrementor controller 490, FIG. 12A showing a circuit for generating the count signal COUNT and the reset signal RESET for controlling the incrementor 478 and FIG. 12B showing a circuit for generating a signal MOVE for transferring data to the output register groups 430 and 432. As described before, the incrementor has three funtions: the first function is to increase the value of the input data by unity, the second is to reset the input data, and the third is to pass the input data without change. The increment function, i.e. the first function to increase the value of the input data by unity, is performed in response to the count signal COUNT and the reset function in response to the reset signal RESET. When the count signal is at the high level, the increment function is performed while the non-increment is performed when the count signal is at the low level. When the reset signal is at the high level, the reset function is carried out. The reset signal is given a preference over the count signal.

The various conditions are selected in response to the stage signals specified by the respective processings. The conditions refer to the synchronized external inputs and the outputs from the second comparison output register group 504. The condition for transferring data to the output register group 474 are the same as that for the control of the incrementor.

FIG. 13 illustrates a processing operation according to the fuel injection signal INJ. Since the time of starting the injection of fuel varies depending on the number of cylinder used, the initial angular position pulses INTLD derived from the reference signal PRS are counted by the register 442 serving as a CYL counter. The result of the counting is compared with the content of the CYL register 404 holding a value corresponding to the number of the cylinders. When the result of counting is greater than or equal to the content of the register 404, "1" is set in the CYL FF 506 of the first comparison output register group 502 and further in the CYLBF 508 of the second group 504. The CYL counter 442 is reset if the content of the CYLBF equals 1. Also, for CYLBF=1, the INJ timer 450 for measuring the fuel injection duration is reset. The content of the timer 450 is always increased unconditionally with time and compared with the content of the INJD register 412 holding the data corresponding to the fuel injection duration. When the content of the timer 450 is greater than or equal to the content of the register 412, "1" is set in the INJFF 522 of the first group 502 and further in the INJBF 524 of the second group 504. The unconditional increment with time is inhibited for INJBF=1. The inverted version of the content of the register INJBF is the fuel injection duration, i.e. the valve opening period of the fuel injector.

FIG. 14 illustrates a processing according to the signal for controlling the ignition. The register 452 serving as the ADV counter is reset by the initial angular position pulse INTLD. The content of the register 452 is increased while the synchronized angular position signal PC is at the high level. The increased content of the register 452 is compared with the content of the register ADV 414 holding the data corresponding to the ignition angle. If the former is greater than or equal to the latter, "1" is set in the register ADVFF 526 of the first group 502 and further in the register ADVBF 528 of the second group 504. The signal ADVD indicating the rising part of the output of the ADVBF resets the DWL counter 454 for instructing the start of conduction. The content of the DWL counter 454 is increased while the synchronized angular position signal PC is at the high level, and then compared with the content of the DWL register 416 holding the data representing the angular position at which the electric conduction takes place, relative to the previous ignition angle. If the former is greater than or equal to the latter, "1" is set in the register DWLFF 530 of the first group 502 and further in the register DWLBF 532 of the second group 504. The output of the DWLBF 532 is the ignition control signal ING1.

FIG. 15 illustrates a processing according to the signal EGR(NIDL). The circuit elements 28 for controlling EGR, to which the signal EGR is supplied, employs a proportional solenoid and therefore the control of EGR is effected by controlling the duty cycles of the input signal. They are the EGRP register 418 for holding the period and the EGRD register 420 for holding the on-duration. The timer used in this processing is the EGR timer 456. During the processing in the stage EGRPSTG, the increment is unconditional. If the content of the EGR timer 456 proves to be greater or equal to the content of the EGRP register 418 as the result of comparison, "1" is set in the EGRPFF 534 of the first register group 502 and further in the EGRPBF 536 of the second register group 504.

During the processing in the stage EGRDSTG, the unconditional non-increment takes place and the EGR timer 456 is reset for EGRPBF=1. If, as a result of comparison, the content of the EGR timer 456 is greater than or equal to the content of the EGRD register 420, "1" is set in the EGRD register 538 of the first group 502 and further in the EGRD register 540 of the second group 504. The inversion of the output of the EGRD register 540 is the control signal EGR.

FIG. 16 illustrates the way of measuring the rotational speed of engine RPM (or vehicle speed VSP) and the processing of the measured results. The measurement is performed by determining a certain measurement duration by the RPMW timer 460 and also by counting the synchronized angular position pulses PC within the determined duration by the same counter.

The content of the RPMW timer 460 for measuring the measurement duration is increased unconditionally and reset when the content of the RPMWBF 552 is "1". If, as a result of comparison, the content of the RPMW timer 460 is greater than or equal to the content of the RPMW register 426, "1" is set in the RPMWFF 550.

In response to the signal RPMWD representing the rising part of the output signal of the RPMWBF 552, the content of the RPM counter 462 representing the result of the count of the pulses PC is transferred to the RPM register 430 of the output register group 474. The RPM counter 462 is reset when the content of the RPMWBF 552 is "1". The processing in the stage VSPSTG is similar to that described above.

The functions of the registers used in the embodiment of this invention will be particularized below in the following table 3.

                  TABLE 3                                                          ______________________________________                                         No. of                                                                         register   function of register                                                ______________________________________                                         402        to hold the digital value corresponding                             (ZERO . REG)                                                                              to zero and to transfer the value to the                                       comparator when required.                                           404        to hold the data CYL representing the                               (CYL . REG)                                                                               number of the used cylinders, the data                                         CYL being used, for example, to produce                                        a signal representing the rotation of the                                      crank shaft through 360°.                                    406        to hold the data INTL representing the                              (INTL . REG)                                                                              crank angle and the angle between a pre-                                       determined crank angular position and the                                      angular position of the sensor for generating                                  the reference signal INTLS. The reference                                      signal PR from the sensor 98 is shifted                                        by a predetermined value in accordance with                                    the data INTL so as to correspond to the                                       predetermined crank angular position.                               408        to hold, as a timer, the data INTV re-                              (INTV . REG)                                                                              presenting the time to measure. If the                                         data INTV is set in the register 408,                                          an interruption signal can be delivered                                        after the lapse of the time.                                        410        to hold the data ENST representing the                              (ENST . REG)                                                                              time used to detect the accidental stopping                                    of the engine.                                                      412        to hold the data INJD representing the                              (INJD . REG)                                                                              valve opening period of the fuel injector.                          414        to hold the data ADV representing the                               (ADV . REG)                                                                               crank angle range measured from the ref-                                       erence angle at which the reference signal is                                  generated to the primary current cut-off                                       angle of the ignition coil.                                         416        to hold the data DWL representing the crank                         (DWL . REG)                                                                               angle range from the angle at which the                                        immediately previous reference signal is                                       generated to the angle at which the primary                                    current is conducted through the ignition                                      coil, in which range the primary current                                       is kept cut off.                                                    418        to hold the data EGRP representing the                              (EGRP . REG)                                                                              pulse period of the pulse current signal                                       EGR for controlling the aperture of the                                        valve of the EGR apparatus.                                         420        to hold the EGRD representing the                                   (EGRD . REG)                                                                              pulse duration of the pulse current signal                                     EGR for controlling the aperture of the                                        valve of the EGR apparatus.                                         422        to hold the data NIDLP representing the                             (NIDLP . REG)                                                                             period of the pulse current signal NIDL                                        for controlling the air regulator provided                                     to control the flow of air through the                                         bypass of the throttle chamber.                                     424        to hold the data NIDLD representing the                             (NIDLD . REG)                                                                             pulse duration of the pulse current signal                                     NIDL.                                                               426        to hold the data RPMW representing the                              (RPMW . REG)                                                                              constant period of time used to detect                                         the rotational speed of the engine.                                 428        to hold the data VSPW representing the                              (VSPW . REG)                                                                              constant period of time used to detect the                                     vehicle speed.                                                      442        to hold the instantaneous number represent-                         (CYLC . REG)                                                                              ing the number of arrivals of the reference                                    signal pulses.                                                      444        to hold the number of the crank angle                               (INTL . REG)                                                                              pulses delivered after the delivery of                                         the reference pulse from the angular                                           position sensor 98.                                                 446        to hold the instantaneous value of the                              (INTVT . REG)                                                                             variable which increases at regular                                            intervals, e.g. every 1024 μsec, after the                                  proper data has been set in the INTV                                           register 408.                                                       448        to hold the instantaneous value of the                              (ENST . REG)                                                                              variable which increases at regular inter-                                     vals, e.g. every 1024 μsec, after the                                       reference pulse has been delivered from                                        the angular position sensor 98. The content                                    of the register 448 is reduced to zero                                         upon reception of the reference pulse.                              450        to hold the instantaneous value of the                              (INJT . REG)                                                                              variable which increases at regular inter-                                     vals, e.g. every 8 μsec, 16 μsec, 32 μsec,                            64 μsec, 128 μsec or 256 μsec, after the                              CYL signal has been delivered. The above                                       interval of time is chosen by the T register.                       452        to hold the instantaneous value of the                              (ADV . REG)                                                                               variable which increases each time the                                         angular position sensor 98 delivers the                                        signal PC representing the rotation of                                         a fixed crank angle, e.g. 0.5 degree,                                          after the reference signal INTLS has been                                      delivered.                                                          454        to hold the instantaneous value of the                              (DWCL . REG)                                                                              variable which increases each time the                                         angular position sensor 98 delivers the                                        crank angle position signal PC after the                                       immediately previous signal INTLS has been                                     delivered.                                                          456        to hold the instantaneous value of the                              (EGRT . REG)                                                                              variable which increases at regular inter-                                     vals, e.g. every 256 μsec, after the signal                                 EGRP has been delivered.                                            458        to hold the instantaneous value of the                              (NIDLT . REG)                                                                             variable which increases at regular inter-                                     vals, e.g. every 256 μsec, after the signal                                 NIDLP has been delivered.                                           460        to hold the instantaneous value of the                              (RPMWT . REG)                                                                             variable which increases at regular intervals                                  of time after the second comparison result                                     holding register 552 has delivered an output                                   pulse.                                                              462        to hold the instantaneous value of the                              (RPMC . REG)                                                                              variable which increases each time the                                         angular position sensor 98 delivers the                                        angular position signal PC representing                                        a fixed crank angle, after the second                                          comparison result holding register 552                                         has delivered an output pulse.                                      430        to hold the data transferred from the                               (RPM . REG)                                                                               register 462 in response to the output                                         signal from the second comparison result                                       holding register 552. The data is delivered                                    onto the data bus in accordance with the                                       address signal and the control instruction                                     from the CPU 114.                                                   464        to hold the instantaneous value of the                              (VSPWT . REG)                                                                             variable which increases at regular intervals                                  of time after the second comparison result                                     holding register 556 has delivered an                                          output.                                                             468        to hold the instantaneous values of the                             (VSPC . REG)                                                                              variable which increase each time one                                          of the pulses corresponding to the rotational                                  speed of the wheel is generated, after                                         the second comparison result holding register                                  556 has delivered an output pulse.                                  432        to hold the data transferred to the                                 (VSP . REG)                                                                               register 468 in response to the output                                         signal of the second comparison holding                                        register 556. The data is delivered onto                                       the data bus in accordance with the address                                    signal and the control instruction from                                        the CPU 114.                                                        506        to have "1" set in if the data of the                               (CYLFF)    register 404 is less than or equal to the                                      data of the register 442.                                           508        to have the signal from the register 506                            (CYLBF)    set in in timing with the clock signal .0.2.                        510        to have "1" set in if the data of the                               (INTLFF)   register 406 is less than or equal to                                          the data of the register 444.                                       512        to have the signal from the register                                (INTLBF)   510 set in in timing with the clock signal                                     .0.2.                                                               514        to have "1" set in if the data of the                               (INTVFF)   register 408 is less than or equal to                                          the data of the register 446.                                       516        to have the signal from the register 514                            (INTVBF)   set in in timing with the clock signal .0.2.                        518        to have "1" set in if the data of the                               (ENSTFF)   register 410 is less than or equal to the                                      data of the register 448.                                           520        to have the signal from the register 518                            (ENSTBF)   set in in timing with the clock signal .0.2.                        522        to have "1" set in if the data of the                               (INJFF)    register 412 is less than or equal to the                                      data of the register 450.                                           524        to have the signal from the register 522                            (INJBF)    set in in timing with the clock signal                                         .0.2.                                                               526        to have "1" set in if the data of the                               (ADVFF)    register 414 is less than or equal to the                                      data of the register 452.                                           528        to have the signal from the register 526                            (ADVBF)    set in in timing with the clock signal .0.2.                        530        to have "1" set in if the data of the                               (DWLFF)    register 416 is less than or equal to                                          the data of the register 454.                                       532        to have the signal from the register 530                            (DWLBF)    set in in timing with the clock signal .0.2.                        534        to have "1" set in if the data of the                               (EGRPFF)   register 418 is less than or equal to the                                      data of the register 456.                                           536        to have the signal from the register 534                            (EGRPBF)   set in in timing with the clock signal .0.2.                        538        to have "1" set in if the data of the                               (EGRDFF)   register 420 is less than or equal to the                                      data of the register 456.                                           540        to have the signal from the register 538                            (EGRDBF)   set in in timing with the clock signal .0.2.                        542        to have "1" set in if the data of the                               (NIDLPFF)  register 422 is less than or equal to the                                      data of the register 458.                                           544        to have the signal from the register 542                            (NIDLPBF)  set in in timing with the clock signal .0.2.                        546        to have "1" set in if the data of the                               (NIDLDFF)  register 424 is less than or equal to the                                      data of the register 458.                                           548        to have the signal from the register 546                            (NIDLDBF)  set in in timing with the clock signal .0.2.                        550        to have "1" set in if the data of the                               (RPMWFF)   register 426 is less than or equal to the                                      data of the register 460.                                           552        to have the signal from the register 550                            (RPMWBF)   set in in timing with the clock signal .0.2.                        554        to have "1" set in if the data of the                               (VSPWFF)   register 428 is less than or equal to the                                      data of the register 464.                                           556        to have the signal from the register 556                            (VSPWBF)   set in in timing with the clock signal .0.2.                        ______________________________________                                    

Now, description will be made of how the reference data is set in the reference register group 470. The registers 402, 404, 406 and 410 have their data set at the time of starting the apparatus as the embodiment of this invention. The values of the data are never changed once they have been set in the registers. The setting of data in the register 408 is performed according to the programmed processing.

The register 412 receives the data INJD representing the value opening duration of the fuel injector 66. The data INJD is determined, for example, as follows. The output signal QA of the air-flow meter 14 is sent through the multiplexer 122 to the analog/digital converter 124. The digital data delivered from the A/D converter 124 is held in a register (not shown). The load data TP is obtained from the above data representing the quantity of sucked air and the data held in the register 430 shown in FIG. 4, through arithmetic operations or on the basis of the information stored in a map fashion. The outputs of the sensor 16 for the temperature of the sucked air, the sensor for the temperature of the cooling water and the sensor for the atmospheric pressure are converted to digital quantities, which are corrected according to the load data TP and the condition of the engine at operation. Let the factor of such a correction be K₁. The voltage of the battery is also converted to a digital quantity. The digital version of the battery voltage is also corrected according to the load data TP. Let the correction factor in this case be TS. Next, the correction by the λ sensor 80 takes place and let the correction factor associated be α. Therefore, the data INJD is given by the following expression.

    INJD=α(K.sub.1 ·TP+TS)

Thus, the valve opening duration of the fuel injector is determined. The above method of determining the data INJD is merely an example and other methods may be employed.

The data ADV representing the ignition timing is set in the register 414. The data ADV is made up, for example, as follows. The map-like ignition data QIG with the data TP and the rotational speed as factors is held in the ROM 118. The data QIG is then subjected to starting correction, water temperature correction and acceleration correction. After these corrections, the data ADV is obtained.

The data DWL for controlling the charging period for the primary current through the ignition coil is set in the register 416. This data DWL is obtained through arithmetic operation from the data ADV and the digital value of the battery voltage.

The data EGRP representing the period of the signal EGR and the data NIDLP representing the period of the signal NIDL are set respectively in the registers 418 and 422. The data EGRP and NIDLP are predetermined.

The data EGRD representing the duration of opening the valve of the EGR (exhaust gas recurrent) apparatus is set in the register 420. As the duration increases, the aperture of the valve increases to increase the rate of recurrence of exhaust gas. The data EGRD is held in the ROM 118 in the form of, for example, a map-like data with the load data TP and the rotational speed as factors. The data is further corrected in accordance with the temperature of the cooling water.

The data NIDLD representing the duration of energizing the air regulator 48 is set in the register 424. The data NIDLD is determined, for example, as a feedback signal derived from such a feedback control that the rotational speed of the engine under no load conditions always equals a preset fixed valve.

The data RPMW and VSPW representing fixed periods of time are set respectively in the registers 426 and 428 at the beginning of the operation of the apparatus.

In the foregoing description of the embodiment of this control apparatus, the output of the air-flow meter is used to control the amount of injected fuel, the advance of ignition angle and the recycle rate of exhaust gas. Any sensor other than the air-flow meter, however, may be employed to detect the condition of the sucked air. For example, a pressure sensor for detecting the pressure in the intake manifold may be used for that purpose.

As described above, according to this invention, the pulse signals received irregularly with respect to the stage cycle are synchronized so that exact detections can be assured.

Further, in the embodiment of this control apparatus described above, since the stage cycle is constituted of major cycles each of which consists of minor cycles, the detection cycle can be controlled in accordance with the precision required. Moreover, since each of the stages for detecting the synchronized signals is processed for a period in the order of a minor cycle, exact detections can be assured even when the engine is operating at a high speed.

Furthermore, the above described embodiment of this control apparatus has a reference register group, an instantaneous register group and a comparison result holding register group and a register is selected from each of the register groups and connected with the comparator in accordance with the outputs of the stage counter, so that so many control functions can be effected by a relatively simple circuit.

FIG. 17 shows in block diagram a circuit of an embodiment of this invention. FIG. 18 shows waveforms useful in explaining the operation of the circuit. In FIG. 17, a processor 1402 comprises a CPU 114, a RAM 116 and a ROM 118. Reference numeral 408 indicates the INTV register shown in FIGS. 4 and 7, for specifying the period T1 of an internal interrupt for the processor 1402; 1404 a counter constituted of the incrementor 478 and the INTV register 446 of the instantaneous register group 472 shown in FIGS. 4 and 7; 1406 an interval interrupt generating circuit constituted of the comparator 480 and the INTVBF register 516; 1405 a register for storing an interrupt factor, e.g. STATUS register shown in FIG. 4; 130 the discrete I/O circuit shown in FIG. 3; 1408 and 1410 well-known one-shot circuits; and 1412 a lamp driving circuit for driving a lamp 1414.

When data representing the period T1 is set in the .[.INTV.]. .Iadd.INTVSTG .Iaddend.register 408 by the processor 1402, the counter 1404 receives the stage signal INTV as a clock signal and performs a count-up operation in accordance with the operation of the incrementor 478 for the constant period T1 of time, that is, until the result of the count-up coincides with the period T1, as seen in FIG. 18(A). Accordingly, the counter 1404 delivers a signal a shown in FIG. 18(A), which is supplied to one of the two inputs of the INTV interrupt generating circuit 1406. On the other hand, since the output of the INTV register 408 is supplied to the other input of the INTV interrupt generating circuit 1406, the circuit 1406 generates an interrupt signal b .Iadd.pulse train .Iaddend.(FIG. 18(B)) at the period T1. The signal b is stored as an interrupt factor in the bit position 4, i.e. 2⁴ bit (shown in FIG. 20A), of the STATUS register (FIG. 4) and then ANDed with the contents of the corresponding 2⁴ bit of the mask register shown in FIG. 4, to supply an interrupt requesting signal IRQ.

FIG. 19 is a flow chart illustrating the operation of the processor when an interrupt occurs. First, to ascertain the interrupt factor, the content of the bit position 4 of the STATUS register is sent to the processor while the interrupt factor is reset at the same time, that is, the content of the bit position 4 of the STATUS register is reset (see the step ○1 in FIG. 19). The interval interrupt factor is alloted to, for example, the bit position 4(2⁴ bit), as shown in FIG. 20A and it is checked or determined whether or not the signal 1 from the INTVBF register 516 (FIGS. 4 and 8) has been held in the bit position 4. If there is held an interval interrupt factor in the bit position, the state of the previous CHECK signal c is checked, that is, whether the state of the previous CHECK signal c is "0" or not, is checked (see step ○2 in FIG. 19). The CHECK signal, represented as a signal c in FIGS. 17 and 18, is supplied from the discrete I/O circuit 130 to the one-shot circuits 1408 and 1410 and alternates between high and low levels at the period T1. Also, as shown in FIG. 20B, the CHECK signal is allocated to the 2⁴ bit of the discrete I/O circuit 130 and can be rewritten by the processor 1402.

The processor 1402, as shown in the steps ○3 and ○4 in FIG. 19, delivers to the discrete circuit 130 the inverted version of the output state of the previous CHECK signal. Therefore, as described above, the CHECK signal c alternately takes ON and OFF states, as shown in FIG. 18(C).

The one-shot circuit 1408 generates a pulse having a duration of T2(T2>T1) which is produced in response to the leading edge of the CHECK signal c while the one-shot circuit 1410 generates a pulse having the same duration T2 which is produced in response to the trailing edge of the CHECK signal, the generated pulses being respectively signals d and e shown in FIGS. 18(D) and 18(E). Since these signals d and e are supplied to an OR gate, the output signal f of the OR gate is as shown in FIG. 18(F).

Accordingly, as long as the processor is operating normally and therefore the CHECK signal takes the ON and OFF state alternately, the STOP signal f, which is the output of the OR gate shown in FIG. 18(F).

Now, when the processor stops its operation for some reason or when it performs an erroneous operation, the processor fails to properly process the interval interrupt so that the CHECK signal, which is the output of the discrete circuit 130, remains in the ON or OFF state. Namely, if the processor commits an error or malfunction at the instant A as shown in FIG. 18, CHECK signal c is no longer generated. Accordingly, the one-shot circuits 1408 and 1410 generate no pulses, the STOP signal f turns OFF, and the lamp driving circuit 1412 is actuated to cause the lamp 1414 to indicate that the processor is in fault. When the fault of the processor is discovered, the driver (automobile driver) may change various automatic control operations into manual ones.

As described above, the fault which may occur in the processor can be detected without fail by a comparatively simple circuit. When the processor fails in its operation, the functions of controlling the fuel injection and the ignition lead angle are considered to be abnormal. It is, therefore, dangerous if a man continues to drive a vehicle with a defective processor. It is necessary to operate a backup circuit for delivering at least control signals essential for safe driving of the vehicle, when the processor is discovered to be defective.

FIG. 21 shows a circuit for actuating such a backup circuit as mentioned above by the use of the STOP signal f derived from the circuit shown in FIG. 17 and for controlling the fuel injection in place of the defective processor. Reference numeral 412 indicates an INJD register for determining the fuel injecting duration under the control of the processor 1402; 1422 a counter constituted of the instantaneous register 450 and the incrementor 478; 480 a comparator; 1000 a backup circuit; 1001 and 1002 AND gates; 1003 an OR gate; 522 and 524 the INJFF register and the INJBF register, respectively; 186 the power amplifier shown in FIG. 3; and 66 the fuel injector. The circuit 1000 may be of any type which can determine the fuel injection duration on the basis of the rotational number N and/or the air-flow rate QA or the negative pressure.

When the processor is operating normally, the STOP signal f is in the ON state so that the output of the INJD register 412 is supplied through the AND gate 1001 to the comparator 480. When the processor fails, the STOP signal f is in the OFF state. Accordingly, the AND gate 1001 is closed, the output of the backup circuit 1000 is supplied through the AND gate 1002 to the comparator 480, and fuel is injected in accordance with the output of the backup circuit.

FIG. 22 shows a circuit for actuating the backup circuit by the use of the STOP signal f and for controlling the ignition lead angle in place of the failed processor. Reference numeral 414 indicates the ADV register; 1424 a counter constituted of the register 452 and the incrementor 478; 480 a comparator; 1010 a backup circuit; 1001-1014 AND gates; 1015 and 1016 OR gates. The backup circuit 1010 may be of any type which can determine the ignition coil condition start lead angle Q_(D) and the ignition coil firing lead angle Q_(A) on the basis of the rotational number N and/or the air-flow rate Q_(A) or the negative pressure in the intake manifold. When the STOP signal f is in the ON state, the outputs of the ADV register 414 and the DWL register, which are set therein from the processor 1402, are selected. While the STOP signal f is in the OFF state, the outputs Q_(D) and Q_(A) of the backup circuit 1010 are selected.

FIG. 23 shows a specific example of the backup circuit shown in FIGS. 21 or 22, in which reference symbols Q_(A) and N denote respectively the 10-bit information representing the air-flow rate measured by the flow meter 14 and the 10-bit information representing the rotational speed of the engine. While the processor 1402 is operating normally, all ten bits of each of the items of information Q_(A) and N are used to perform a control operation with high precision. On the other hand, when the processor fails, a high precision control cannot be expected and it is only necessary to perform such controls as are essential for safe driving of the vehicle. Therefore, it is needless to use all ten bits of each item of information, that is, it suffices to use the three higher order bits, i.e. bits 7, 8 and 9. The three higher order bits of each of the signals Q_(A) and N are converted to decimal numbers by a decoder. Now, if the three higher order bits of the signals Q_(A) and N are respectively 1,0,1 and 1,0,0, those binary quantities are converted respectively to 5 and 4 in decimal notation through decoding. Accordingly, the address (5, 4) in the memory M is selected so that the information stored in the address (5, 4) and corresponding to a word controls the fuel injection and the ignition lead angle.

FIG. 24 shows a backup circuit of simple configuration without using the signals Q_(A) and N. The backup circuit is shown as adapted for the control of, for example, fuel injection as in FIG. 21. Since the stop signal f is at high level (1) during the normal operation of the processor 1402, all the gates of an AND gate group 1001A are open so that the contents of the INJD register 412 are supplied through the AND gate group 1001A to an OR gate 1003. In this case, all the gates of an AND gate group 1002A are closed since they receive the signal f through an inverter. When the signal f goes low (0) owing to the failure of the processor 1402, all the gates of the AND gate group 1001A are closed while all the gates of the AND gate group 1002A are opened. As a result, the AND gate group 1002A delivers a predetermined type of bit information (0,1, . . . 0,1, in FIG. 24), which is supplied to the OR gate 1003 to control the fuel injection in place of the failed processor 1402.

The present invention can be also achieved by an alternative embodiment in that there is provided a soft-counter program, a detecting program for detecting that values counted under the soft-counter program have reached a predetermined value, and means for clearing the counted contents by an interrupt signal with a constant period which corresponds to the signal b of the above-mentioned embodiments, in which the abnormal operation of a central processing unit can be detected by the fact that the counted contents have reached a predetermined high level so that the counted contents are no longer cleared when the central processing unit fails to process normally the interrupt signals.

As described above, according to this invention, a fault in the processor serving as the center of an automobile control apparatus can be detected by a simple circuit construction and moreover, as explained with the embodiment, the peripheral control circuits except the processor can be switched over to the fail-safe side, whereby an automobile control apparatus having high safety can be provided.

Namely, according to the embodiment, the controls of fuel injection and ignition lead can be performed by the backup circuit when the processor is operating abnormally, whereby safe driving can be continued. Moreover, the lamp is lit up when the operation of the processor is abnormal, so that the driver may be warned against an accident due to the defect of the processor. 

What we claim is:
 1. An electronic control apparatus for an internal combustion engine comprisinga processor having a central processing unit, a random access memory and a read-only memory .Iadd.utilized for controlling operational conditions of said engine.Iaddend.; means for generating an interrupt signal .Iadd.pulse train .Iaddend.having a predetermined period for causing an interrupt request signal to be applied to said processor; and means for detecting said processor to be in a state of its normal operation and generating an output signal in response to said processor generating a signal equivalent to a pulse train having a pulse duration substantially equal to said predetermined period.
 2. An electronic control apparatus according to claim 1, wherein said interrupt signal generating means includesan interval register in which said processor sets data representative of said predetermined period, a counter the contents of which are sequentially incremented in accordance with a clock signal supplied thereto, and an interrupt request signal generating circuit for generating said interrupt signal in response to the contents of said counter reaching a value corresponding to said data representative of said predetermined period stored in said interval register.
 3. An apparatus as claimed in claim 1 or claim 2, wherein said detecting means includesa first pulse generating circuit for receiving said pulse train and for generating a single pulse having a predetermined duration in response to the leading edge of a pulse of said pulse train, a second pulse generating circuit for receiving said pulse train and for generating a single pulse having a predetermined duration in response to the trailing edge of a pulse of said pulse train, and an OR circuit for receiving the outputs of said first and second pulse generating circuits to form a logical sum and for delivering a continuously constant level signal in response to said pulse train being applied to said first and second pulse generating circuits.
 4. An apparatus according to claim 1, further comprisinga backup circuit for controlling the supply of fuel to the engine, said backup circuit delivering a predetermined signal to control the supply of fuel in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow rate of air drawn into the engine; and a circuit for actuating said backup circuit in response to the absence of the output signal of said detecting means.
 5. An apparatus according to claim 1, further comprisinga backup circuit for controlling ignition timing, said backup circuit delivering a predetermined signal to control ignition timing in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow-rate of air drawn into the engine; and a circuit for actuating said backup circuit in response to the absence of the output signal of said detecting means.
 6. An apparatus according to claim 1, further comprising a backup circuit for controlling the supply of fuel to the engine, said backup circuit delivering a previously fixed signal to control the supply of fuel to the engine; anda circuit for actuating said backup circuit in response to the absence of the output signal of said detecting means.
 7. An apparatus according to claim 1, further comprisinga backup circuit for controlling ignition timing, said backup circuit delivering a previously fixed signal to control ignition timing; and a circuit for actuating said backup circuit in response to the absence of the output signal of said detecting means.
 8. An electronic engine control apparatus adapted for use with a combustion engine comprisingdigital processing means having a central processing unit, a random access memory and a read-only memory, utilized for controlling operational conditions of said engine; interrupting signal generating means for generating an interrupting signal .Iadd.pulse train .Iaddend.having a predetermined period to be applied to said digital processing means in response to delivery of data representative of an interval period corresponding to said predetermined period from said digital processing means; and detecting means for detecting said digital processing means to be in a state of its normal operation in response to said digital processing means producing output data corresponding to a pulse train having a pulse duration substantially equal to said predetermined period of said detecting means.
 9. An electronic engine control apparatus as claimed in claim 8, wherein said interrupting signal generating means includesan interval register for storing the data representative of said interval period from said digital processing means; counting means the contents of which are successively incremented in response to a clock signal which is applied to said counting means; and an interrupt generator for generating an interrupting signal, said interrupt generator including a comparator, inputs of which are coupled to the outputs of said interval register and said counting means, for comparing the output of said interval register with the output of said counting means.
 10. An electronic engine control apparatus as claimed in claim 9, wherein said detecting means includesa first pulse generating circuit for generating a single pulse having a predetermined duration in response to the leading edge of a pulse of said pulse train received from said processing means; a second pulse generating circuit for generating a single pulse having a predetermined duration in response to the trailing edge of a pulse of said pulse train received from said processing means; and an OR gate for receiving the outputs of said first and second pulse generating circuits to form a logical sum and for outputting a signal having a continuously constant level in response to said pulse train being applied to said first and second pulse generating circuits.
 11. An electronic engine control apparatus as claimed in claim 10, further comprisinga register holding data representing the valve opening period of a fuel injector for said engine; a backup circuit outputting a desired data signal to control the fuel injection of said engine, said backup circuit receiving a data signal representing the rotational speed of said engine and a data signal representing the flow rate of air drawn into said engine; gate means for gating either of the outputs of said backup circuit and said register in response to the output signal from said detecting means, inputs of said gate means being coupled to the outputs of said backup circuit and said register, and the output of said gate means being coupled to the input of said comparator; and an actuator for controlling the fuel injection of said engine, said actuator being coupled to receive the output of said comparator.
 12. An electronic engine control apparatus as claimed in claim 10, further comprisinga register holding data representing a crank angle of said engine; a backup circuit outputting a desired data signal to control the ignition timing of said engine, said backup circuit receiving a data signal representing the rotational speed of said engine and a data signal representing the flow rate of air drawn into said engine; gating means for gating either of the outputs of said backup circuit and said register in response to the output signal from said detecting means, the inputs of said gating means being coupled to the outputs of said backup circuit and said register, and the output of said gating means being coupled to the input of said comparator; and an actuator for controlling the ignition timing of said engine, said actuator being coupled to receive the output of said comparator.
 13. An electronic engine control apparatus as claimed in claim 10, further comprisinga register holding data representing the valve opening period of a fuel injector for said engine; a backup circuit outputting predetermined fixed data for controlling the fuel injection of said engine; gating means for gating either of the outputs of said backup circuit and said register in response to the output signal from said detecting means, the inputs of said gating means being coupled to the outputs of said backup circuit and said register, and the output of said gating means being coupled to the input of said comparator; and an actuator for controlling the fuel injection of said engine, said actuator being coupled to receive the output of said comparator.
 14. An electronic engine control apparatus as claimed in claim 10, further comprisinga register holding data representing a crank angle of said engine; a backup circuit outputting predetermined fixed data for controlling the ignition timing of said engine; gating means for gating either of the outputs of said backup circuit and said register in response to the output signal from said detecting means, the inputs of said gating means being coupled to the outputs of said backup circuit and said register, and the output of said gating means being coupled to the input of said comparator; and an actuator for controlling the ignition timing of said engine, said actuator being coupled to receive the output of said comparator.
 15. An electronic control apparatus for an internal combustion engine having:sensor means for producing signals representative of operating conditions of said engine; actuator means for controlling respective energy conversion functions of said engine in response to control signals applied thereto; an input/output unit coupled to receive signals produced by said sensor means and to deliver control signals to said actuator means, and a data processing unit, coupled to said input/output unit, for carrying out engine control data processing operations in accordance with signals produced by said sensor means and thereby generating engine control codes that are coupled to said input/output unit; said input/output unit comprising: first means for generating an engine control timing signal pattern through which operational events of said engine are controlled; second means, coupled to said data processing unit, for storing said engine control codes; third means, coupled to said first means, for generating respective engine timing codes the values of which are selectively modified by said engine control timing pattern; fourth means, coupled to said second and third means, for comparing respective ones of said engine control codes with respective ones of said engine timing codes and producing respective output signals when said respective engine control codes define a prescribed relationship with respect to said engine timing codes; fifth means, coupled to said fourth means, for producing control signals to be coupled to said actuator means in response to the output signals produced by said fourth means; sixth means, responsive to the generation of an output signal by said fourth means, for generating an interrupt signal of a prescribed duration to be coupled to said data processing unit; and seventh means, coupled to said data processing unit, for generating a signal representative of a malfunction of said data processing unit, in response to said data processing unit failing to generate a prescribed signal representable by a pulse train having a pulse duration corresponding to said prescribed duration.
 16. An electronic control apparatus according to claim 15, wherein one of said engine control codes stored by said second means is representative of said prescribed duration.
 17. An electronic control apparatus according to claim 15, further comprisinga backup circuit for controlling the supply of fuel to the engine, said backup circuit delivering a prescribed signal to control the supply of fuel in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow rate of air drawn into the engine, derived in accordance with outputs of respective sensor means; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 18. An electronic control apparatus according to claim 15, further comprisinga backup circuit for controlling ignition timing, said backup circuit delivering a prescribed signal to control ignition timing in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow-rate of air drawn into the engine derived in accordance with outputs of respective sensor means; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 19. An electronic control apparatus according to claim 15, further comprising:a backup circuit for controlling the supply of fuel to the engine; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 20. An electronic control apparatus according to claim 15, further comprising:a backup circuit for controlling ignition timing; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 21. An electronic control apparatus according to claim 15, wherein one of the codes stored by said second means is representative of the period of time during which a respective actuator means is to supply fuel to said engine, and further including:a backup circuit for generating a prescribed data signal to control said respective actuator means to supply fuel to said engine, said backup circuit receiving a data signal representative of the flow of air drawn into the engine and a data signal representative of the rotational speed of the engine crankshaft; and gate means for coupling either of the outputs of said backup circuit and the fuel supply code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 22. An electronic control apparatus according to claim 15, wherein one of the codes stored by said second means is representative of the crank angle of the engine crankshaft, and further including:a backup circuit for generating a prescribed data signal operate a respective actuator means to control the ignition timing of the engine, said backup circuit receiving a data signal representative of the rotational speed of the engine crankshaft and a data signal representative of the flow rate of air drawn into the engine; and gate means for coupling either of the outputs of the backup circuit and the crank angle code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 23. An electronic control apparatus according to claim 15, wherein one of the codes stored by said second means is representative of the period of time during which a respective actuator means is to supply fuel to said engine, and further including:a backup circuit for generating a prescribed data code to control said respective actuator means to supply fuel to said engine; and gate means for coupling either of the outputs of said backup circuit and the fuel supply code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 24. An electronic control apparatus according to claim 15, wherein one of the codes stored by said second means is representative of the crank angle of the engine crankshaft, and further including:a backup circuit for generating a prescribed data code to control a respective actuator means to control the ignition timing of the engine; and gate means for coupling either of the outputs of said backup circuit and the crank angle code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 25. An electronic control apparatus for an internal combustion engine having:sensor means for producing signals representative of operating conditions of said engine; actuator means for controlling respective energy conversion functions of said engine in response to control signals applied thereto; an input/output unit coupled to receive signals produced by said sensor means and to deliver control signals to said actuator means, and a data processing unit, coupled to said input/output unit, for carrying out engine control data processing operations in accordance with signals produced by said sensor means and thereby generating engine control codes that are coupled to said input/output unit; said input/output unit comprising: first means for generating an engine control timing signal pattern through which operational events of said engine are controlled; second means, coupled to said data processing unit, for storing said engine control codes; third means, coupled to said first means, for generating respective engine timing codes the values of which are selectively modified by said engine control timing pattern; fourth means, coupled to said second and third means, for comparing respective ones of said engine control codes with respective ones of said engine timing codes and producing respective output signals when said respective engine control codes define a prescribed relationship with respect to said engine timing codes;fifth means, coupled to said fourth means, for producing control signals to be coupled to said actuator means in response to the output signals produced by said fourth means; sixth means, responsive to a selected one of the respective output signals produced by said fourth means, for generating an interrupt signal to be coupled to said data processing unit; and seventh means, coupled to said data processing unit, for generating a signal representative of a malfunction of said data processing unit, in response to said data processing unit failing to generate a prescribed signal the state of which changes within a prescribed period of time following its previous change of state.
 26. An electronic control apparatus according to claim 25, wherein one of said engine control codes stored by said second means is representative of a prescribed period of time, and said interrupt signal has a repetition period corresponding to said prescribed period of time.
 27. An electronic control apparatus according to claim 26, further comprisinga backup circuit for controlling the supply of fuel to the engine, said backup circuit delivering a prescribed signal to control the supply of fuel in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow rate of air drawn into the engine, derived in accordance with outputs of respective sensor means; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 28. An electronic control apparatus according to claim 26, further comprisinga backup circuit for controlling ignition timing, said backup circuit delivering a prescribed signal to control ignition timing in response to a signal representing the rotational speed of the engine crankshaft and a signal representing the flow-rate of air drawn into the engine derived in accordance with outputs of respective sensor means; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 29. An electronic control apparatus according to claim 26, further comprising:a backup circuit for controlling the supply of fuel to the engine; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 30. An electronic control apparatus according to claim 26, further comprising:a backup circuit for controlling ignition timing; and means, responsive to the signal generated by said seventh means, for activating said backup circuit.
 31. An electronic control apparatus according to claim 25, wherein one of the codes stored by said second means is representative of the period of time during which a respective actuator means is to supply fuel to said engine, and further including:a backup circuit for generating a prescribed data signal to control said respective actuator means to supply fuel to said engine, said backup circuit receiving a data signal representative of the flow rate of air drawn into the engine and a data signal representative of the rotational speed of the engine crankshaft; and gate means for coupling either of the outputs of said backup circuit and the fuel supply code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 32. An electronic control apparatus according to claim 25, wherein one of the codes stored by said second means is representative of the crank angle of the engine crankshaft, and further including:a backup circuit for generating a prescribed data signal operate a respective actuator means to control the ignition timing of the engine, said backup circuit receiving a data signal representative of the rotational speed of the engine crankshaft and a data signal representative of the flow rate of air drawn into the engine; and gate means for coupling either of the outputs of the backup circuit and the crank angle code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 33. An electronic control apparatus according to claim 25, wherein one of the codes stored by said second means is representative of the period of time during which a respective actuator means is to supply fuel to said engine, and further including:a backup circuit for generating a prescribed data code to control said respective actuator means to supply fuel to said engine; and gate means for coupling either of the outputs of said backup circuit and the fuel supply code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 34. An electronic control apparatus according to claim 25, wherein one of the codes stored by said second means is representative of the crank angle of the engine crankshaft, and further including:a backup circuit for generating a prescribed data code to control a respective actuator means to control the ignition timing of the engine; and gate means for coupling either of the outputs of said backup circuit and the crank angle code stored by said second means to said fourth means in dependence upon the generation of a signal by said seventh means.
 35. For use in a processor-controlled apparatus for controlling the operation of an internal combustion engine in response to sensor signals representative of operating conditions of the engine supplied thereto, an arrangement for detecting .[.misoperation.]. .Iadd.a malfunction .Iaddend.of said apparatus comprising:first means, coupled to said processor, for periodically generating an interrupt signal and causing an interrupt request signal to be supplied to said processor; and second means, coupled to said processor, for generating an output signal representative of a malfunction of said apparatus in response to said processor failing to generate a signal equivalent to a periodic pulse train the period of which corresponds to the period of said interrupt signal.
 36. For use in a processor-controlled apparatus for controlling the operation of an internal combustion engine in response to sensor signals representative of operating conditions of the engine supplied thereto, an arrangement for detecting .[.misoperation.]. .Iadd.a malfunction .Iaddend.of said apparatus comprising:first means, coupled to said processor, for generating a first data signal representative of the frequency at which an interrupt signal for causing an interrupt request to be coupled to said processor is to be generated; second means for storing a second data signal the value of which is periodically changed at a constant frequency; third means, coupled to said first and second means, for generating said interrupt signal in response to the value of said second data signal having a predetermined relationship with said first data signal; and fourth means, coupled to said processor, for generating an output signal representative of a malfunction of said apparatus in response to said processor failing to generate a signal equivalent to a periodic pulse train the frequency of which corresponds to the frequency represented by said first data signal.
 37. For use in a processor-controlled apparatus for controlling the operation of an internal combustion engine in response to sensor signals representative of operating conditions of the engine supplied thereto, an arrangement for detecting normal operation of said apparatus comprising:first means, coupled to said processor, for generating a first data signal representative of the frequency at which an interrupt signal for causing an interrupt request to be coupled to said processor is to be generated; second means for storing a second data signal the value of which is periodically changed at a constant frequency; third means, coupled to said first and second means, for generating said interrupt signal in response to the value of said second data signal having a predetermined relationship with said first data signal; and fourth means, coupled to said processor, for generating an output signal representative of normal operation of said apparatus in response to said processor generating a signal equivalent to a periodic pulse train the frequency of which corresponds to the frequency represented by said first data signal. .Iadd.
 38. An electronic control apparatus for an internal combustion engine comprising:a processor having a central processing unit, a random access memory and a read-only memory utilized for controlling operational conditions of said engine; means for generating an interrupt signal pulse train having a predetermined period for causing an interrupt request signal to be applied to said processor; and means for detecting said processor to be in a state of its normal operation and for producing an indication when said processor is not generating a signal equivalent to a pulse train having a pulse duration controlled in accordance with said interrupt request signal. .Iaddend. 